如何在雄辯中定義一對一的關係？

在Laravel Eloquent中，定義一對一關係需先設置數據庫外鍵並使用hasOne和belongsTo方法關聯模型。 1. 在phones表中通過foreignId('user_id')->unique()建立唯一外鍵指向users表；2. 在User模型中定義public function phone() { return $this->hasOne(Phone::class); }表示用戶擁有一部電話；3. 在Phone模型中定義public function user() { return $this->belongsTo(User::class); }表示電話屬於一個用戶；4. 可通過$user->phone->number訪問關聯數據，或使用$user->phone()->create()創建記錄；5. 若外鍵名非默認user_id，可在第二個參數指定自定義字段名。正確配置後Eloquent將自動處理關聯操作，完整實現一對一關係。

In Laravel's Eloquent ORM, defining a one-to-one relationship is straightforward and follows a simple convention. This type of relationship exists when one record in a database table is associated with exactly one record in another table.

1. Database Setup

First, ensure your database schema supports the one-to-one relationship. For example, let's say a User has one Phone . You'd set up your tables like this:

 // In a migration for 'users' table
Schema::create('users', function (Blueprint $table) {
    $table->id();
    $table->string('name');
    $table->timestamps();
});

// In a migration for 'phones' table
Schema::create('phones', function (Blueprint $table) {
    $table->id();
    $table->foreignId('user_id')->unique(); // user_id is foreign key and unique
    $table->string('number');
    $table->timestamps();

    $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
});

? The user_id in the phones table must be unique to enforce one-to-one mapping.

2. Define the Relationship in Eloquent Models

Now, define the relationship in your models.

In the User model:

 <?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    public function phone()
    {
        return $this->hasOne(Phone::class);
    }
}

✅ hasOne() means "a user has one phone".

In the Phone model:

 <?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Phone extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

✅ belongsTo() means "a phone belongs to a user".

3. Usage Examples

Once defined, you can use the relationship like this:

 // Get a user's phone
$user = User::find(1);
echo $user->phone->number;

// Get the user from a phone
$phone = Phone::find(1);
echo $phone->user->name;

// Create a phone for a user
$user = User::find(1);
$user->phone()->create([
    'number' => '555-1234'
]);

? Eloquent automatically uses the model name and _id suffix (eg, user_id ) as the foreign key unless you specify otherwise.

Optional: Custom Foreign Key

If your foreign key is not user_id , you can specify it:

 return $this->hasOne(Phone::class, 'custom_user_id');

Or in belongsTo :

 return $this->belongsTo(User::class, 'custom_user_id');

That's it. One-to-one relationships in Eloquent are clean and intuitive—just use hasOne on the "owner" side and belongsTo on the "dependent" side. Basically just set up the right migration and model methods, and Eloquent handles the rest.

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